Real Firefox and Real Chrome. The iOS versions is just a wrapper around the painfully bad mobile Safari.
Safari seems to take this seriously instead of the race to the bottom on performance and resource consumption. I also like features like how Safari extensions are now 1st class apps and its declarative content blocker (1Blocker X being best in class imo).
What makes Safari so bad in your eyes?
(full disclosure: I am a happy Safari user, and the content blocking API is good enough that I tolerate it but I do miss uBlock for sure)
But for example I have a script that can convert Adblock format rules (like Easylist) into content blocker rules.
The problem with the declarative API is that 1) it’s just not as flexible as uBlock, especially in a world where billions are being poured into bypassing blockers and 2) each blocker extension is limited to 50k rules which is not enough (some apps work around this by registering multiple blocker extensions, but frankly this limitation is BS and should not exist to begin with) and 3) blockers don’t run with the browser, so you have to open the app every so often to update the blocking rules.
The rendering engine is poor. It's probably the browser I have the most trouble with when doing frontend work. iframe scrolling is broken, it's historically suffered from some frustrating flexbox bugs (see https://github.com/philipwalton/flexbugs#flexbug-11), its Can I use... score lags behind Firefox and Chrome. For a while, it didn't support service workers properly.
I could go on.